Drawing on factors identified in the literature, this study explored in-the-moment associations of social, emotional, and temporal contexts and perceived marijuana availability with desire to use the drug, using momentary sampling methodology with young people who frequently use marijuana. Forty-one adolescent/young adult medical outpatients aged 15 to 24 years who reported using marijuana at least twice a week completed 2,912 brief questionnaires on a handheld computer in response to signals emitted at random four to six times a day for 2 weeks. The questionnaires assessed, for the moment when signaled, desire to use marijuana, location, companionship, perceived ease of getting marijuana (availability), positive affect, and negative affect. Participants reported any desire to use marijuana on 1,528 reports (55%). Companionship, perceived availability, and positive affect were independently associated with having any desire to use marijuana. Once desire to use marijuana was present, time of day, positive affect, and negative affect were independently associated with strength of desire. By collecting data in real time, in real life, this study highlights the importance of examining and intervening on emotional, environmental, and temporal contexts for youth who frequently use marijuana in order to reduce their desire to use the drug.